Skorpion Zinc: Mine-to-metal zinc production via solvent extraction

Anglo Research

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Skorpion Zinc: Mine-to-metal zinc production

via solvent extraction

Kathy SoleAnglo Research, South Africa

Herman Fuls, Jürgen GnoinskiSkorpion Zinc, Namibia

H

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Traditional Zinc Processing

• Usually present as sulphide• Amenable to upgrading• Roast-Leach-Electrowin process

Oxides and silicates considered “untreatable”

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Skorpion Zinc

Oxide/silicate: Zn 10 - 40%Si 26%Fe 2 - 3%Some Cl and F

• First application of Zn SX to primary processing

• Silicate leaching technology

• First metal May 2003

• 150 000 t/a SHG zinc (>99.995% purity)

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Overview

• Electrolyte requirements for Zn EW

• Skorpion Zinc flowsheet

• Challenges and process improvements duringfirst 5 years of operation

• Comparison of design and actual performance

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Skorpion Zinc

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Skorpion Zinc

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Advance Electrolyte Specification

Element Concentration Element Concentration(mg/l) (μg/l)

Zn > 90 000 Ga 3Mn 2 000 Ge < 10Cd < 0.05 As < 10Co < 0.05 Sn < 1Ni < 0.05 Sb < 1Fe < 5 Te < 1Cl < 0.1 Tl 25F < 0.02

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Simplified Skorpion Flowsheet

Base metals, Cl, F

CaCO3

Zinc silicate oxide ore Comminution

Leach

Neutralisatn

Thickening

Zn SX

Zn EW

SHG Zn cathode (>99.995% Zn)

H2SO4

Fe, Al, Si

H2SO4

O/F

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Silicate Leaching

• High SiO2 in ore

• Avoid conditions for silica gel formation

• Minimise Zn losses in filtration

dilute leach liquor (30 g/L Zn)

upgrade and purify by SX

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Zn Extraction by D2EHPA

1 2 3 4 5 6 7 8 00

20

40

60

80

100Fe(lll)

RO

RO OHP

O

Zn Ca MnCu Co

NiMg

Equilibrium pH

Extr

actio

n (%

) Cd

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Skorpion Zn SX Circuit

W1

Raffinate

E1E2E3 W3W2 S1 S2

PLSSO

Zn EW

> 99.995 % Zn

H2O

SOSE

ScOLO

R1

6 M HCl

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Selectivity of SX

Extraction Wash Scrub Strip/Regen EW

ZnFeCuCaMgMnKNaCdCoNiSnAsSbClF

From Técnicas Reunidas

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Specification Skorpionfor AE (mg/l) electrolyte (mg/l)

Zn > 90 000 ~ 120 000Cd < 0.05 0.012Fe < 5 < 5Mn < 3000 2500Co < 0.05 0.07Ni < 0.05 0.07Ca — ~ 50Cl < 100 56F < 20 3

Element

Full-Scale SX Process Performance

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Full-Scale SX Process Performance

• Selectivity matches theory

• Capacity exceeds design — 107 % Zn transfer

***Pic carbon columns

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Challenges

• Organic transfer to EW

• Solids in PLS

• Health of organic phase

• Fire risk – single stream: 100% production loss

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Process ImprovementsMinimisation of organic transfer to EW

No D2EHPA 5 mg/L D2EHPA

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Process ImprovementsMinimisation of organic transfer to EW

Advance electrolyte processed through

• aftersettler

• flotation column

• activated carbon filter/coalescers(lead-lag configuration)

< 1 mg/L OE

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0

300

600

900

[M]

in A

E (u

g/L)

Running time (months)

NiCu

Process ImprovementsDeportment of impurities to electrolyte

200

400

600

[M]

in P

LS (

mg/

L)

Cu

Jan Mar May Jul Sep Nov 2007

Ni

SX Feed Advance electrolyte

Running time (months) Running time (months)

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Electrowinning of Zinc

−1.18Mn2+ + 2 e → Mn

−0.76Zn2+ + 2 e → Zn

−0.40Cd2+ + 2 e → Cd

−0.35PbSO4 + 2 e → Pb + SO42−

−0.28Co2+ + 2 e → Co

−0.26Ni2+ + 2 e → Ni0.002 H+ + 2 e → H2

0.34Cu2+ + 2 e → Cu

Eo (V)Half-cell reduction

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• Solids in PLS~100 mg/L TSS (target <10 mg/L TSS) excessive crud formation

• Linked to excursions of Ni, Co

• High organic consumption

Process ImprovementsDeportment of impurities to electrolyte

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Process ImprovementsControl of solids’ deportment to SX

Original design• thickener

• clarifier

• sand filters

Process improvements• PLS ponds

• avoid colloidal silica formation

• pH control of leach

• avoid leach plant downtime

• reduce mixer air entrainment

• Roymec pinned-bed clarifier

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Process ImprovementsControl of solids’ deportment to SXPinned-bed clarifier <10 mg/L TSS

0

100

200

300

1 5 9 13 17 21 25 29Running time (days)

TSS

(mg/

L)

PLS inPLS out

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PLS and Electrolyte Composition

Al 300 82 190Ca 650 660 50Cd 100 330 <0.05 0.01Cl 5000 1030 <100 50Co 100 18 <0.05 0.02Cu 700 500 <0.05 0.09F 200 40 <20 7Fe 5 1.5 <5 <5Mg 200 1040Mn 500 2120 3000 2200Ni 800 330 <0.05 0.08Si 40 70Zn 30 000 38 000 90 000 117 000

Design ActualAE (mg/L)

Element Design ActualPLS (mg/L)

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Advantages of Zn SX

• High Si in ore

Ø Dilute leach solution to avoid silica gelØ Minimise soluble zinc losses in filtrate

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Advantages of Zn SX

• High Si in ore

• EW very sensitive to impuritiesØ Reject Cu, Ni, Co, Cd, Mn, MgØ Reject F, ClØ Reject Ca

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Advantages of Zn SX

• High Si in ore

• EW very sensitive to impurities

• UpgradeØ 30 g/l Zn in PLSØ > 100 g/l Zn in AE

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Advantages of Zn SX

• High Si in ore

• EW very sensitive to impurities

• Upgrade

• SHG ZnØ > 99.995 % purity

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Cd 30 0Cu 10 7Fe 20 3Pb 30 25Sn 2 2Zn 999950 999963

Element SHG spec.* Skorpion(ppm) (ppm)

SHG Zinc Cathode

* British standard, 1996

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Product Quality150 000 t/a

>99.995% Zn

SHG Zn

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Conclusions

• Breakthrough technology for zinc oxide treatment –“untreatable” ore

• First mine-to-metal operation

• Robust technology

• SX process considered a technical success

• Consistent production of 150 000 t/a SHG Zn

• Amongst world’s highest quality and lowest costzinc producers (2007 C1 US¢ 32/lb Zn)

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Acknowledgements

Skorpion Zinc

Anglo Base Metals

Sole 2001, Proceedings 6th World Congress Chemical Engineering, Melbourne

Fuls et al. 2005, Proceedings ISEC 2005, Beijing

Gnoinski et al. 2005, Proceedings Lead-Zinc 2005, Osaka

Sole et al. 2008, Proceedings ISEC 2008, Tucson, AZ